The pesent invention relates to a headbox of a papermaking machine, particularly the configuration of the turbulence insert in a headbox of a papermaking machine.
Headboxes of papermaking machines are generally described in German Patent No. DE 4,019,593 A1 to J. M. Voith GmbH, which issued on Jan. 9, 1992.
Tube bundles are utilized as rectifiers and turbulence generators in hydraulic headboxes of papermaking machines. The input cross section of an individual tube is circular and the tubes are arranged and worked in such a way that the outlet cross section is, for example, honeycomb-shaped, pentagonal, or even rectangular. The individual rows of a tube bundle packet may be displaced with respect to one another or may be arranged in flush manner. The individual tubes are closed up to the ends of the tube, i.e., their suspension flows do not have a hydraulic connection.
Viewed hydraulically, the following problems result at the outlet of the turbulence insert. Each jet from each individual tube has a velocity profile, which has very small values at the edges, corresponding to the profile of a tube flow. These edge zones are accelerated by pulse exchange with the core flow and with adjacent flows after release from the turbulence insert into the nozzle. In the case of flows from tubes positioned at the edges, the pulse exchange cannot take place on the edge side or the outside. The stays between the individual tubes thus have a long after-running extent with a smaller velocity than in the after-running of the tube center. This velocity profile cannot be completely equilibrated within the nozzle and leads to an adverse effect in jet quality in the free jet after leaving the nozzle and thus produces disturbances in the paper formation.